Lid and Catback -- How much HP?
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Teching In
Joined: Apr 2005
Posts: 49
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From: Bangor, ME
Lid and Catback -- How much HP? If I install an SLP LMII exhaust and lid what sort of HP gain might I see at the rear wheels? I'm just looking for a rough estimate, like 5 hp or something more like 20 hp. Also, is there anything in particular wrong with the SLP lid? Should it be avoided? And are these a good pair of first modifications for as small amount of money as possible? Thanks!
You should gain about 20 hp with a lid and catback. On my old '99, I went from 297 rwhp stock to 317 with the lid and catback. Didn't dyno my '02 with before and after, but I picked up about 0.25 - 0.30 and 2.5 - 3.0 mph at the track which would indicate about 20 hp.
I've normally heard that a good catback and lid should get you around 20 hp to the wheels. Of course this is just a figure though, some will get more, others less. But 20 rwhp seems to be the average from what I've heard. The lid should get you about 10 hp and the catback about 15, so there's your 20 to the wheels accounting for drivetrain loss.
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Originally Posted by XRno1
Ok, thanks! By the way, Scotty-Z, what type of wheels are those that you have and where could I find some?
TECH Fanatic
Joined: Nov 2001
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From: I-L-L-I-N-O-I-S
Since nobody seems to have a relevant before and after, here ya go...
298rwhp & 320rwtq 100% factory stock SAE corrected on Speed Inc's dynojet @ 1,200ish miles...
323rwhp & 342rwtq with ONLY the additions of a Direct-Flo intake lid and 3" GMMG cat-back system SAE corrected on the very same Speed Inc dynojet only 750 miles later (weather was also similar even though already accounted for by correction factor).
Leaning out the Air/Fuel Ratio a little with a Mass Air Flow Translator slightly bumped those #'s up to 325rwhp & 346rwtq (again, everything all the same).
This was all done to my 2002 M6 Z28 BTW...
Hope that helps and you can more than take my word for this,
Mike
298rwhp & 320rwtq 100% factory stock SAE corrected on Speed Inc's dynojet @ 1,200ish miles...
323rwhp & 342rwtq with ONLY the additions of a Direct-Flo intake lid and 3" GMMG cat-back system SAE corrected on the very same Speed Inc dynojet only 750 miles later (weather was also similar even though already accounted for by correction factor).
Leaning out the Air/Fuel Ratio a little with a Mass Air Flow Translator slightly bumped those #'s up to 325rwhp & 346rwtq (again, everything all the same).
This was all done to my 2002 M6 Z28 BTW...
Hope that helps and you can more than take my word for this,
Mike
4200FT 
I have owned two LS1's in which I dynoed with just a lid and LM.
99Z28 Hardtop M6
324 RWHP 334 RWTQ
13.2 @ 106
00 WS6 M6
326 RWHP 335 RWTQ
13.0 @ 108
This is with both cars on stock tires, stock weight, stock everything else.
Both cars only have made 3 passes down the track EVER
99Z28 Hardtop M6
324 RWHP 334 RWTQ
13.2 @ 106
00 WS6 M6
326 RWHP 335 RWTQ
13.0 @ 108
This is with both cars on stock tires, stock weight, stock everything else.
Both cars only have made 3 passes down the track EVER